The laws of hametz from the Bible and Talmud apply only to food made from the "five species of grain." During the Middle Ages, however, the custom arose among Ashkenazic Jews of not eating kitniyot on Pesah. The reason behind this custom is obscure, but it may have been the possibility of confusing dried, ground, legumes with regular flour. The customary prohibition extends also to some foods which are not really legumes in a botanical sense. One rabbinic definition of kitniyot is "edible seeds of annual plants which are not covered with flesh".
Thus, we do not eat peas, beans, corn, rice, millet, mustard, peanuts, lentils, buckwheat, chickpeas or sesame. Some authorities permit the use of oil made from these vegetables. Furthermore, the rabbis were not sure whether or not peanuts are kitniyot. It should be noted that peanuts are unquestionably legumes; the question is whether or not they fit the Jewish traditional definition of kitniyot.
Thus, on the basis of a double doubt, peanut oil is sometimes available with rabbinical approval for Pesah. Naturally, only oil which has such approval should be used. In 1984, the Rabbinical Assembly permitted the eating of peanuts on Pesah. Nevertheless, peanut products, such a peanut oil or peanut butter, should be eaten on Pesah only if they were made under rabbinical supervision, or if it can be determined that they were made without any contact with hametz.
Vegetarians or other people with special dietary needs may have an especially difficult time on Pesah if they are not able to eat kitniyot. I would suggest that people in that situation consider eating kitniyot on Pesah, following these guidelines:
1. Purchasing kitniyot in their raw natural state is very much to be preferred to the use of processed foods containing kitniyot.
2. If processed foods are to be used, one should ascertain that ingredients which may be truly hametz do not constitute more than 1/60 of the whole. If it is not possible to ascertain the ingredients of a processed food to such a degree of precision, then the food should not be used on Pesah.
3. In either case above, kitniyot foods should be purchased before Pesah, so that the year-round rules of bittul (annulment of a prohibited substance) may apply, and not the more stringent Pesah rules (which do not permit bittul at all).
4. In a household in which some people eat kitniyot on Pesah and others do not, one may wish to use separate utensils for the cooking and serving of kitniyot foods. However, in the last analysis, regular Pesah utensils may be used for kitniyot, without compromising the pesachdik character of those utensils.
